The correct answer is the first option. Electron is not found in the nucleus of an atom. The sub-atomic particles of an atom are the proton, electron and the neutron. An electron has a charge of -1 and a smaller mass than a proton. Proton has the same mass with the neutron. The ratio between the mass of a proton and an electron is about 2000. An electron has an equal value but negative charge with the proton.